
In
materials science, the strength of a material is its ability to withstand an applied
stress without failure. Yield strength refers to the point on the engineering stress-strain curve (as opposed to true stress-strain curve) beyond which the material begins deformation that cannot be reversed upon removal of the loading. Ultimate strength refers to the point on the engineering stress-strain curve corresponding to the maximum stress. The applied stress may be
tensile,
compressive, or
shear.
A material's strength is dependent on its microstructure. The engineering processes to which a material is subjected can alter this microstructure. The variety of
strengthening mechanisms that alter the strength of a material includes
work hardening,
solid solution strengthening,
precipitation hardening and
grain boundary strengthening and can be quantified and qualitatively explained. However, strengthening mechanisms are accompanied by the caveat that some mechanical properties of the material may degenerate in an attempt to make the material stronger. For example, in grain boundary strengthening, although
yield strength is maximized with decreasing grain size, ultimately, very small grain sizes make the material brittle. In general, the yield strength of a material is an adequate indicator of the material's mechanical strength. Considered in tandem with the fact that the yield strength is the parameter that predicts
plastic deformation in the material, one can make informed decisions on how to increase the strength of a material depending its microstructural properties and the desired end effect. Strength is considered in terms of
compressive strength,
tensile strength, and
shear strength, namely the limit states of
compressive stress,
tensile stress and
shear stress, respectively. The effects of dynamic loading is probably the most important practical part of the strength of materials, especially the problem of
fatigue. Repeated loading often initiates brittle cracks, which grow slowly until failure occurs.
However, the term strength of materials most often refers to various methods of calculating stresses in structural members, such as beams, columns and shafts. The methods that can be employed to predict the response of a structure under loading and its susceptibility to various failure modes may take into account various properties of the materials other than material (yield or ultimate) strength. For example failure in buckling is dependent on material stiffness (Young's Modulus